1. Field of the Invention
The present invention relates to a method of warning of the onset of pipe sticking during rotary drilling operations.
2. Description of the Related Art
In rotary drilling operations a drill string made of a series of pipes joined end to end with a drill bit attached to the bottom is rotated in the borehole and drilled material is carried from the bottom of the borehole by means of drilling fluid which is pumped down inside the drill string and returns to the surface in the annular space outside the drill string carrying the drilled material with it. From time to time the drill string can become stuck due to interaction with the borehole. The drill string becomes stuck when the torque or overpull which can be applied to the drill string at the surface is insufficient to free the drill string from its interaction with the borehole.
Stuck pipe is undesirable since it often results in long periods of lost drilling time and occasionally lost equipment in the borehole when it is not possible to free the drill string which must then be cut and the borehole sidetracked to avoid the stuck part of the drill string remaining in the hole. Methods have been proposed for identifying situations when sticking is starting to occur. These can involve monitoring parameters such as hookload at the surface when pulling the drill string out of the hole. However, none of these is known to provide advance warning of the onset of pipe sticking.